It requires at least Ant 1.9.8 (I use Ant 1.10.5), otherwise you'll get this error message:
javac doesn't support the "nativeheaderdir" attribute

NativeTaglet doesn't compile because it extended com.sun.tools.doclets.Taglet (which works with Java 8 but not with Java 11) and it extends now jdk.javadoc.doclet.Taglet (which works with Java 11 but not with Java 8).